I have a use case where I need to fetch the ids of my entire solr collection. For that, with solrj, I use the Streaming API like this :
CloudSolrServer server = new CloudSolrServer("zkHost1:2181,zkHost2:2181,zkHost3:2181");
SolrQuery query = new SolrQuery("*:*");
server.queryAndStreamResponse(tmpQuery, handler);
Where handler is a class that implements StreamingResponseCallback, ommited in my code for brevity.
Now, the Spring data repositories abstraction give me the ability to search by pages, by cursors, but I can't seem to find a way to handle the streaming use case.
Is there a workaround ?
SolrTemplate allows to access the underlying SolrClient in a callback style. So you could use that one to work around the current limitations.
The result conversion using the MappingSolrConverter available via the SolrTemplate is broken at the moment (I need to check why) - but you get the idea of how to do it.
solrTemplate.execute(new SolrCallback<Void>() {
#Override
public Void doInSolr(SolrClient solrClient) throws SolrServerException, IOException {
SolrQuery sq = new SolrQuery("*:*");
solrClient.queryAndStreamResponse("collection1", sq, new StreamingResponseCallback() {
#Override
public void streamSolrDocument(SolrDocument doc) {
// the bean conversion fails atm
// ExampleSolrBean bean = solrTemplate.getConverter().read(ExampleSolrBean.class, doc);
System.out.println(doc);
}
#Override
public void streamDocListInfo(long numFound, long start, Float maxScore) {
// do something useful
}
});
return null;
}
});
I have some problem with guava funnel , I read this article https://code.google.com/p/guava-libraries/wiki/HashingExplained and others , but I don't know how I can use funnel when my class contains not only primitive types.
Funnel<Person> personFunnel = new Funnel<Person>() {
#Override
public void funnel(Person person, PrimitiveSink into) {
into
.putInt(person.id)
.putString(person.firstName, Charsets.UTF_8)
.putString(person.lastName, Charsets.UTF_8)
.putInt(birthYear)
//.putObject(myObject,myObjectFunnel);I want to do something like this
}
};
after I need to do like this
HashFunction hf = Hashing.md5();
HashCode hc = hf.newHasher()
.putObject(person, personFunnel)
.hash();
PrimitiveSink class hasn't putObject method , only Hasher class has it.
I can transform myObject to byte array and use putBytes method , but probably somebody knows better approach.
You're right: at the moment, it's not possible to do it following the API chained methods only.
But I see that you have a myObjectFunnel. So why not use it?
What about:
Funnel<Person> personFunnel = new Funnel<Person>() {
#Override
public void funnel(Person person, PrimitiveSink into) {
into
.putInt(person.id)
.putString(person.firstName, Charsets.UTF_8)
.putString(person.lastName, Charsets.UTF_8)
.putInt(birthYear);
myObjectFunnel.funnel(myObject, into);
}
};
Could somebody be kind enough to give me an example of how to Send and Register custom objects between classes using MVVM Light's Messenger or point me to a tutorial that covers this (preferably a concrete example)? I've been trying to use Messenger to pass an object in my project to another class but I've never been successful at it. I've looked online for examples but haven't found anything that shows me what I need. Thanks.
Jesse Liberty of Microsoft has a great concrete walk through on how to make use of the messaging within MVVM Light. The premise is to create a class which will act as your message type, subscribe, then publish.
public class GoToPageMessage
{
public string PageName { get; set; }
}
This will essentially send the message based on the above type/class...
private object GoToPage2()
{
var msg = new GoToPageMessage() { PageName = "Page2" };
Messenger.Default.Send<GoToPageMessage>( msg );
return null;
}
Now you can register for the given message type, which is the same class defined above and provide the method which will get called when the message is received, in this instance ReceiveMessage.
Messenger.Default.Register<GoToPageMessage>
(
this,
( action ) => ReceiveMessage( action )
);
private object ReceiveMessage( GoToPageMessage action )
{
StringBuilder sb = new StringBuilder( "/Views/" );
sb.Append( action.PageName );
sb.Append( ".xaml" );
NavigationService.Navigate(
new System.Uri( sb.ToString(),
System.UriKind.Relative ) );
return null;
}
I found THIS and THIS very useful. For the second reference use the Next Page button at the end to take you to examples they made.
Does anyone know the best way to refactor a God-object?
Its not as simple as breaking it into a number of smaller classes, because there is a high method coupling. If I pull out one method, i usually end up pulling every other method out.
It's like Jenga. You will need patience and a steady hand, otherwise you have to recreate everything from scratch. Which is not bad, per se - sometimes one needs to throw away code.
Other advice:
Think before pulling out methods: on what data does this method operate? What responsibility does it have?
Try to maintain the interface of the god class at first and delegate calls to the new extracted classes. In the end the god class should be a pure facade without own logic. Then you can keep it for convenience or throw it away and start to use the new classes only
Unit Tests help: write tests for each method before extracting it to assure you don't break functionality
I assume "God Object" means a huge class (measured in lines of code).
The basic idea is to extract parts of its functions into other classes.
In order to find those you can look for
fields/parameters that often get used together. They might move together into a new class
methods (or parts of methods) that use only a small subset of the fields in the class, the might move into a class containing just those field.
primitive types (int, String, boolean). They often are really value objects before their coming out. Once they are value object, they often attract methods.
look at the usage of the god object. Are there different methods used by different clients? Those might go in separate interfaces. Those intefaces might in turn have separate implementations.
For actually doing these changes you should have some infrastructure and tools at your command:
Tests: Have a (possibly generated) exhaustive set of tests ready that you can run often. Be extremely careful with changes you do without tests. I do those, but limit them to things like extract method, which I can do completely with a single IDE action.
Version Control: You want to have a version control that allows you to commit every 2 minutes, without really slowing you down. SVN doesn't really work. Git does.
Mikado Method: The idea of the Mikado Method is to try a change. If it works great. If not take note what is breaking, add them as dependency to the change you started with. Rollback you changes. In the resulting graph, repeat the process with a node that has no dependencies yet. http://mikadomethod.wordpress.com/book/
According to the book "Object Oriented Metrics in Practice" by Lanza and Marinescu, The God Class design flaw refers to classes that tend to centralize the intelligence of the system. A God Class performs too much work on its own, delegating only minor details to a set of trivial classes and using the data from other classes.
The detection of a God Class is based on three main characteristics:
They heavily access data of other simpler classes, either directly or using accessor methods.
They are large and complex
They have a lot of non-communicative behavior i.e., there is a low
cohesion between the methods belonging to that class.
Refactoring a God Class is a complex task, as this disharmony is often a cumulative effect of other disharmonies that occur at the method level. Therefore, performing such a refactoring requires additional and more fine-grained information about the methods of the class, and sometimes even about its inheritance context. A first approach is to identify clusters of methods and attributes that are tied together and to extract these islands into separate classes.
Split Up God Class method from the book "Object-Oriented Reengineering Patterns" proposes to incrementally redistribute the responsibilities of the God Class either to its collaborating classes or to new classes that are pulled out of the God Class.
The book "Working Effectively with Legacy Code" presents some techniques such as Sprout Method, Sprout Class, Wrap Method to be able to test the legacy systems that can be used to support the refactoring of God Classes.
What I would do, is to sub-group methods in the God Class which utilize the same class properties as inputs or outputs. After that, I would split the class into sub-classes, where each sub-class will hold the methods in a sub-group, and the properties which these methods utilize.
That way, each new class will be smaller and more coherent (meaning that all their methods will work on similar class properties). Moreover, there will be less dependency for each new class we generated. After that, we can further reduce those dependencies since we can now understand the code better.
In general, I would say that there are a couple of different methods according to the situation at hand. As an example, let's say that you have a god class named "LoginManager" that validates user information, updates "OnlineUserService" so the user is added to the online user list, and returns login-specific data (such as Welcome screen and one time offers)to the client.
So your class will look something like this:
import java.util.ArrayList;
import java.util.List;
public class LoginManager {
public void handleLogin(String hashedUserId, String hashedUserPassword){
String userId = decryptHashedString(hashedUserId);
String userPassword = decryptHashedString(hashedUserPassword);
if(!validateUser(userId, userPassword)){ return; }
updateOnlineUserService(userId);
sendCustomizedLoginMessage(userId);
sendOneTimeOffer(userId);
}
public String decryptHashedString(String hashedString){
String userId = "";
//TODO Decrypt hashed string for 150 lines of code...
return userId;
}
public boolean validateUser(String userId, String userPassword){
//validate for 100 lines of code...
List<String> userIdList = getUserIdList();
if(!isUserIdValid(userId,userIdList)){return false;}
if(!isPasswordCorrect(userId,userPassword)){return false;}
return true;
}
private List<String> getUserIdList() {
List<String> userIdList = new ArrayList<>();
//TODO: Add implementation details
return userIdList;
}
private boolean isPasswordCorrect(String userId, String userPassword) {
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
private boolean isUserIdValid(String userId, List<String> userIdList) {
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
public void updateOnlineUserService(String userId){
//TODO updateOnlineUserService for 100 lines of code...
}
public void sendCustomizedLoginMessage(String userId){
//TODO sendCustomizedLoginMessage for 50 lines of code...
}
public void sendOneTimeOffer(String userId){
//TODO sendOneTimeOffer for 100 lines of code...
}}
Now we can see that this class will be huge and complex. It is not a God class by book definition yet, since class fields are commonly used among methods now. But for the sake of argument, we can treat it as a God class and start refactoring.
One of the solutions is to create separate small classes which are used as members in the main class. Another thing you could add, could be separating different behaviors in different interfaces and their respective classes. Hide implementation details in classes by making those methods "private". And use those interfaces in the main class to do its bidding.
So at the end, RefactoredLoginManager will look like this:
public class RefactoredLoginManager {
IDecryptHandler decryptHandler;
IValidateHandler validateHandler;
IOnlineUserServiceNotifier onlineUserServiceNotifier;
IClientDataSender clientDataSender;
public void handleLogin(String hashedUserId, String hashedUserPassword){
String userId = decryptHandler.decryptHashedString(hashedUserId);
String userPassword = decryptHandler.decryptHashedString(hashedUserPassword);
if(!validateHandler.validateUser(userId, userPassword)){ return; }
onlineUserServiceNotifier.updateOnlineUserService(userId);
clientDataSender.sendCustomizedLoginMessage(userId);
clientDataSender.sendOneTimeOffer(userId);
}
}
DecryptHandler:
public class DecryptHandler implements IDecryptHandler {
public String decryptHashedString(String hashedString){
String userId = "";
//TODO Decrypt hashed string for 150 lines of code...
return userId;
}
}
public interface IDecryptHandler {
String decryptHashedString(String hashedString);
}
ValidateHandler:
public class ValidateHandler implements IValidateHandler {
public boolean validateUser(String userId, String userPassword){
//validate for 100 lines of code...
List<String> userIdList = getUserIdList();
if(!isUserIdValid(userId,userIdList)){return false;}
if(!isPasswordCorrect(userId,userPassword)){return false;}
return true;
}
private List<String> getUserIdList() {
List<String> userIdList = new ArrayList<>();
//TODO: Add implementation details
return userIdList;
}
private boolean isPasswordCorrect(String userId, String userPassword)
{
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
private boolean isUserIdValid(String userId, List<String> userIdList)
{
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
}
Important thing to note here is that the interfaces () only has to include the methods used by other classes. So IValidateHandler looks as simple as this:
public interface IValidateHandler {
boolean validateUser(String userId, String userPassword);
}
OnlineUserServiceNotifier:
public class OnlineUserServiceNotifier implements
IOnlineUserServiceNotifier {
public void updateOnlineUserService(String userId){
//TODO updateOnlineUserService for 100 lines of code...
}
}
public interface IOnlineUserServiceNotifier {
void updateOnlineUserService(String userId);
}
ClientDataSender:
public class ClientDataSender implements IClientDataSender {
public void sendCustomizedLoginMessage(String userId){
//TODO sendCustomizedLoginMessage for 50 lines of code...
}
public void sendOneTimeOffer(String userId){
//TODO sendOneTimeOffer for 100 lines of code...
}
}
Since both methods are accessed in LoginHandler, interface has to include both methods:
public interface IClientDataSender {
void sendCustomizedLoginMessage(String userId);
void sendOneTimeOffer(String userId);
}
There are really two topics here:
Given a God class, how its members be rationally partitioned into subsets? The fundamental idea is to group elements by conceptual coherency (often indicated by frequent co-usage in client modules) and by forced dependencies. Obviously the details of this are specific to the system being refactored. The outcome is a desired partition (set of groups) of God class elements.
Given a desired partition, actually making the change. This is difficult if the code base has any scale. Doing this manually, you are almost forced to retain the God class while you modify its accessors to instead call new classes formed from the partitions. And of course you need to test, test, test because it is easy to make a mistake when manually making these changes. When all accesses to the God class are gone, you can finally remove it. This sounds great in theory but it takes a long time in practice if you are facing thousands of compilation units, and you have to get the team members to stop adding accesses to the God interface while you do this. One can, however, apply automated refactoring tools to implement this; with such a tool you specify the partition to the tool and it then modifies the code base in a reliable way. Our DMS can implement this Refactoring C++ God Classes and has been used to make such changes across systems with 3,000 compilation units.
I am working in J2EE 5 using JPA, I have a working solution but I'm looking to clean up the structure.
I am using EntityListeners on some of the JPA objects I am persisting, the listeners are fairly generic but depend on the beans implementing an interface, this works great if you remember to add the interface.
I have not been able to determine a way to tie the EntityListener and the Interface together so that I would get an exception that lead in the right direction, or even better a compile time error.
#Entity
#EntityListener({CreateByListener.class})
public class Note implements CreatorInterface{
private String message;....
private String creator;
....
}
public interface CreatorInterface{
public void setCreator(String creator);
}
public class CreateByListener {
#PrePersist
public void dataPersist(CreatorInterface data){
SUser user = LoginModule.getUser();
data.setCreator(user.getName());
}
}
This functions exactly the way I want it to, except when a new class is created and it uses the CreateByListener but does not implement the CreatorInterface.
When this happens a class cast exception is thrown somewhere deep from within the JPA engine and only if I happen to remember this symptom can I figure out what went wrong.
I have not been able to figure a way to require the interface or test for the presence of the interface before the listener would be fired.
Any ideas would be appreciated.
#PrePersist
public void dataPersist(Object data){
if (!(data instanceof CreatorInterface)) {
throw new IllegalArgumentException("The class "
+ data.getClass()
+ " should implement CreatorInterface");
}
CreatorInterface creatorInterface = (CreatorInterface) data;
SUser user = LoginModule.getUser();
creatorInterface.setCreator(user.getName());
}
This does basically the same thing as what you're doing, but at least you'll have a more readable error message indicating what's wrong, instead of the ClassCastException.